In process metrology, e.g., in chemical, biotechnological, pharmaceutical, and food industry processes, as well as in environmental metrology, such automated analyzers are used to determine a measurand in a liquid sample. Such analyzers may, for example, be used for the monitoring and optimization of the cleaning performance in a sewage treatment plant, for monitoring drinking water, or for monitoring quality of foodstuffs. For example, the proportion of a specific substance, which is also termed an analyte, in a sample liquid such as a liquid mixture, emulsion, suspension, gas, or gas mixture is measured and monitored. Analytes may, for example, be ions such as ammonium, phosphate, silicate, nitrate, calcium, sodium, or chloride, or biological or biochemical compounds, e.g., hormones, or even micro-organisms. Other parameters that are determined using analyzers in process metrology, for example, in the field of monitoring water, are cumulative parameters such as the total organic carbon (TOC), total nitrogen (TM), total phosphorus (TP), or the chemical oxygen demand (COD). Analyzers may, for example, be designed as cabinet devices or buoys.
The sample to be analyzed is often treated inside analyzers by adding one or more reagents, thus provoking a chemical reaction in the reaction mixture formed in this manner. The reagents are preferably selected in order to render the chemical reaction verifiable by physical methods, e.g., by optical measurements, by means of potentiometric or amperometric sensors, or through a conductivity measurement. By means of a measuring sensor, measured values of a measurand that is correlated with the actual analytical parameter (such as COD) to be determined is detected. The chemical reaction may, for example, cause a coloring or a change in color which may be detected using optical means. In such cases, the intensity of the color is a measure of the parameter to be determined. As the measurand correlated with the parameter to be determined, absorption or extinction of the treated sample may, for example, be ascertained by photometric means by feeding electromagnetic radiation, such as visible light, from a radiation source into the liquid sample, and receiving it with a suitable receiver after transmission through the liquid sample. The receiver generates a measurement signal, which depends upon the intensity of the received radiation, and from which the parameter to be determined can be derived for example, by means of a calibration function or table. The parameter value is generally derived by means of measuring electronics, such as a computer that is programmed to determine a measured value of the parameter from the measuring signal using the calibration function or table, and display, save, and/or output the measured value via an interface to a higher-level unit.
In order to use such methods of analysis in an automated way, e.g., in the industrial sector or for monitoring a sewage treatment plant or a body of water outdoors, it is desirable to provide an analyzer that automatically executes the required analytical processes. In addition to sufficient measuring precision, the most important requirements for such an analyzer are robustness, ease of use, low maintenance requirements, and the guarantee of sufficient occupational and environmental safety.
Automatic analyzers are known in the state of the art. For example, DE 102 22 822 A1, DE 102 27 032 A1, and DE 10 2009 029305 A1 disclose generic analyzers for determining one or more parameters of a sample liquid. Such analyzers are each designed as a cabinet device containing measuring and control electronics, a supply tank for reagents, standard solutions, and cleaning liquids, pumps to feed and dose the liquid sample and the reagent or reagents into a measuring cell, and a measuring sensor for optical measurements of the sample exposed to the reagent or reagents in the measuring cell, or a reaction mixture formed therefrom. Controlled by the measuring and control electronics, the reagents, standard solutions, or cleaning liquids are conveyed from the supply tanks and transported into the measuring cell. Correspondingly, used liquid is transferred from the measuring cell into a waste container.
Particularly in applications in the fields of environmental analytics or water management, the sample liquid can contain a particle load to be monitored by means of an automated analyzer. The entrained particles can be filtered out of the sample liquid for example, when sampling from the measuring point so that the sample supplied to the analyzer for analysis is free of particles, and there is, accordingly, no danger of the fluid lines or valves of the analyzer becoming obstructed or blocked by any particles entrained by the sample. The chemical composition of the particle load of a sample liquid is, however, part of certain parameters like digestion parameters such as COD or TP, so that filtering out the particles from the sample before performing the analysis would significantly distort the analytical results. Generally, the sample liquid is therefore analyzed with the inclusion of its particle load. The liquid lines of the analyzer which come into contact with the sample liquid must be designed for this. In locations at which a high flow speed generally predominates, the probability of blockage by particles entrained in the sample liquid is less than at locations in which the sample liquid dwells for a long time where particles can settle. This is, in particular, the case in the measuring cell of the analyzer. The blocking of valves and fluid lines requires regular servicing measures and/or the regular exchange of valves and fluid lines.